Previously known scarifiers for scarifying the interior of a concrete pipe consisted of a moveable vehicle equipped with rotating nozzles positioned adjacent to the interior surface of pipe which impart high pressure jets against the interior surface to remove contaminated and corroded material. The removal of such material leaves a fresh concrete surface which can then be sealed with polyvinyl chloride to prevent any future deterioration of the interior surface. With a scarifier as disclosed in our U.S. Pat. No. 6,206,016 which has a nozzle assembly at the distal end of an arm which positions the nozzle assembly adjacent the interior surface of the pipe, a swath is cut into the pipe surface as the vehicle moves down the pipe. If the material removed falls into the path of the vehicle then, when the vehicle reverses and retraces its path to scarify a new swath adjacent the previous one, it will rise up and down as it runs over the material previously removed by scarifying and cause the swath to move vertically and leave some areas with contaminated or corroded material. For example, some sewer lines have tile embedded in concrete extending part-way or all the way up the sewer wall. Scarifying each swath of the tile along the length of the pipe results in broken pieces of tile falling down on the sewer floor. Reversing to scarify a new swath requires removal of the pieces of tile from the previous swath in order to prevent generating an uneven swath and, thus, leaving regions of corroded and contaminated material on the wall.
Accordingly, it is an object of the invention to provide a scarifier of an interior surface of a pipe which is unaffected by the removal of large pieces of material from the interior surface.